View details for Beta

A measure of the relative volatility of a player's EqA or EqERA forecast, as determined from his comparables. The Beta for an average major league player is 1.00; players with Beta's higher than 1.00 have more volatile forecasts than others ("riskier"), while Betas lower than 1.00 represent less volatile forecasts ("less risky").

Betas are adjusted for the amount of playing time that a player is expected to receive. Thus, a player's Beta will not be higher simply because he's expected to receive less playing time (as a relief pitcher might as compared with a starter, for example), which naturally produces more variance because of higher sample sizes.
Betas may be unreliable for players with few appropriate comparables.